1. Field of the Invention
The present invention relates to a novel metal-organic polymer composite structure, particularly a porous metal-organic polymer composite structure, which can be utilized as functional materials such as catalysts, fixed catalysts, membrane reactors, antistatic plastics and other applications, and a method for producing the same.
2. Prior Art
Ultrafine metal particles including noble metal particles are widely used as catalysts, and it is known that the smaller the particle size is, the higher the catalyst activity per unit weight is. In this case, since an ultrafine metal particle having a particle size of nm order tends to coagulate due to bonding of metal atoms on its surface and it is difficult for the particle to exist in stable manner without any treatment, protection and stabilization using a surfactant and a polymer such as poly(N-vinyl-2-pyrrolidone), poly(2-vinylpyridine) and the like have been tried (Mathias Brust et al., J. Chem. Soc., Chem. Commun., 801, 1994; Naoki Toshima et. al., Chemistry Letters, 1245, 1985). Since ultrafine metal particles thus obtained are usually in a uniform solution, separation from a reaction product is difficult when the particles are used as a catalyst, and for industrial use, a support such as silica gel, polymer or the like is desired. Therefore, it is preferable that the support is composed of a microporous material having a large specific surface area, and consequently, inorganic materials such as silica gel, activated carbon, alumina and the like have been hitherto used. However, these inorganic materials have problems in molding properties and processing properties since they are powders themselves, and for use as a film or membrane, a support by a polymer is required.
Typical examples of methods for producing a microporous film composed of a polymer include the following.
(1) Japanese Patent Application Laid-Open (JPA) No. 1,739/1989 PA1 (2) JPA No. 279,741/1990 PA1 (3) JPA No. 287,084/1993
Described is a method for producing a porous material by microphase separation of a block copolymer composed of a styrene derivative and a conjugated diene or acrylate derivative, and by hydrolysis and treatment of the conjugated diene or acrylate derivative with plasma containing oxygen.
Described is a method in which a mixture of a first polymer having an ionic-bonding functional group on each end of the polymer and a second polymer having a functional group on each end capable of bonding to the afore-said functional group of the first polymer is subjected to a solution casting, one phase of the microphase-separated structure formed in the resulting film is treated with a base or acid to cut the bonding of the block copolymer, and the treated phase is extracted with a solvent.
Described is method for producing a porous film having a pore size of several hundreds nm which has expectantly the possibility as a carrier for a catalyst. This method is characterized in that the film has a bicontinuous structure of various microphase-separated structures to be formed by a block copolymer, one component is decomposed or eluted, and the pore size distribution is very narrow due to the bicontinuous structure.
As for fixing ultrafine metal particles on such a support, although physical adsorption on the surface of the support is most simple, the supported ultrafine metal particles tend to flow out of the system in such method.
For preventing it, ultrafine metal particles are preferably fixed on the support through some chemical bond. As a specific method for chemically fixing ultrafine metal particles, there has been reported a method in which a support obtained by modification with imino diacetate on the surface of a copolymer of styrene and divinylbenzene is used, and then palladium ions are reduced in a water/methanol mixed solution to form palladium fine particles on the support (H. Hirai, S. Komatuzaki, and N. Toshima; Bull. Chem. Soc. Jpn., 57, 488-494, 1984). While a number of methods are thus known for ultrafine metal particles supported on the surface of a polymer, from the viewpoint of stability of ultrafine metal particles on support, supported particle inside the support is more preferable than that on the support.
As methods for introducing ultrafine metal particles inside a polymer, there are known, for example, a method in which poly(2-vinylpyridine) phase of a poly(2-vinylpyridine) polystyrene block copolymer is crosslinked with 1,4-diiodobutane, then, fine crystals of silver iodide are deposited therein, and the crystals are reduced by photoreduction so as to form ultrafine silver particles (R. Saito, S. Okamura and K. Ishizu, Polymer, 1993, 34-6, 1189). A method is also known in which a palladium (II) acetylacetonate complex is dissolved in a methacrylic acid monomer, polymerized and solidified with benzoyl peroxide. Then, the solidified substance is heated to form ultrafine metal particles (Y. Nakao, Kobunshi, 43, December, pp 852-855, 1994). However, the former is a peculiar method utilizing the photoreduction of silver halide fine crystal, and therefore, this method can not be generally applied to a wide range of metals including noble metals such as platinum, palladium and rhodium useful as a catalyst and other applications. The latter method, based on a synthesizing and crosslinking reaction of a homopolymer, is also inappropriate because it cannot form a porous material to be used as a catalyst and other applications.